The present invention relates generally to direct current electrical circuits and warning systems for such circuits which indicate that the circuit is operating properly by actuating an indicator, generally a light, for a predetermined period of time commencing upon the supply of power to the circuit.
Monitoring systems are well known which indicate that an electrical circuit connected to a sensor or device being monitored and which is connected to the circuit are operating properly by turning on or actuating an indicator. The most common type of indicator is a light. Such systems are commonly in use in the electrical systems for machinery, power systems and motor vehicles.
Aircraft are a category of vehicles in which such monitoring systems are widely used. Aircraft systems of all types, including monitoring systems, are designed to minimize weight and energy usage. For example, electrical circuits in aircraft frequently use the body of the aircraft as one of the two electrical conductors necessary for completion of an electric circuit. In this case, the aircraft body is referred to as xe2x80x9cground.xe2x80x9d In some aircraft, particularly those having a body which is made of a material which is not a conductor of electricity, an electrical conductor is used as ground. In either case, the non-ground conductor is a wire or cable which, is generally connected to the positive terminal of the direct current (xe2x80x9cDCxe2x80x9d) power supply. The other, negative, terminal of the power supply is connected to the ground. Any electrical device or sub-circuit must be connected to both the positive terminal or to a conductor that is, and to ground.
Aircraft monitoring systems frequently use an indicator such as a light, frequently referred to in the industry as a lamp, and a sensor of some type which is normally open. When the adverse condition which is being monitored occurs, the open sensor closes completing the circuit and the light is turned on. For example, this is what happens when the fuel in most automobiles drops below a predetermined level.
Some items being monitored are sufficiently important that the electrical continuity of the electrical conductor(s), connecting the sensor to the power supply, is checked every time the power to the circuit is turned on. The lack of continuity indicates that the sensor and anything else connected to the circuit, will not operate. The lack of continuity is generally due to a broken or disconnected electrical conductor. The checking or testing of circuit continuity requires that the circuit temporarily be closed or xe2x80x9cshortedxe2x80x9d at or as close as possible to the monitoring sensor. If upon the closing of the circuit, the indicator is actuated, the circuit has electrical continuity, or if there is no indication then there is a problem as continuity has been lost. The testing of circuit continuity in this manner simulates the sensor having detected the adverse condition which it was designed to detect. The testing of the circuit by the closing or shorting of a monitoring circuit is commonly accomplished automatically by test devices, such as a test circuit connected to the monitoring circuit.
In order to perform its task the test circuit must have electrical power. This may be accomplished by connecting the test circuit to the power supply by its own circuit, i.e., its own conductor and ground. This would result in an additional conductor being used. The use of an additional conductor can be avoided by connecting the test circuit to the monitoring circuit itself, i.e., by connecting the test circuit in parallel with the monitoring circuit. The present invention relates to test circuits of the type where the test circuit is connected to the same conductor and ground as the monitoring circuit thereby causing the monitoring circuit to supply power to both the sensor and to the test circuit.
The condition of aircraft engine lubricating oil is one of many conditions which are commonly monitored in aircraft. Chip detectors are placed in the oil lubrication system which detect the presence of electrically conductive metallic particles above a certain size, or an amount of particles, greater than the amount of particles which always occur due to normal wear during use and which are referred to as xe2x80x9cwear particlesxe2x80x9d. The occurrence of such large particles or an accumulation of larger than normal particles is an indication that a possible dangerous failure of some type may occur. If that condition occurs, an indicator is actuated in the aircraft cockpit alerting the aircraft crew that there is a problem. The chip detector includes two electrically conductive members having a gap between them. Normally the gap is not filled or closed thus forming an open electrical circuit. When the gap is filled as a result of the adverse condition, i.e., one or more electrically sufficiently large conductive chips bridge the gap and close the circuit. Chip detectors may, in some cases, be placed in an aircraft lubricating system where the oil level is adequate for lubricating an engine or transmission but the level is not sufficient at the chip detector location for the chip detector gap to be immersed in the oil and, thus, being incapable of detecting a chip. It is for this reason that an oil level sensor may be placed at an appropriate location proximate to the chip detector so that indication will be given if the oil is below a predetermined level which would result in the chip detector being inoperable. It must be emphasized that this oil level sensor is separate and distinct from the engine oil level sensor which detects whether or not the oil level has dropped below a level which is acceptable for lubrication.
The present invention may also be used to provide an indication that there is an acceptable oil level for lubrication systems for other remotely located devices such as a gearbox.
In order for the chip detector to be operable, not only must the monitoring circuit have continuity but the oil level at the chip detector must be adequate.
In some cases, it is not necessary to measure sensor oil level as the sensor is located in the aircraft lubrication system at a point where it is always immersed in oil when the oil level is adequate for engine lubrication.
The present invention is being described using a sensor which detects metallic chips which are electrically conductive by way of example only. As will readily be understood by those skilled in the art, the present invention is applicable to any sensor, or similar device, which completes a DC circuit when the condition being monitored occurs, or which can be adapted to complete such a circuit.
In order to save weight or to retrofit existing aircraft with chip detector oil level sensors, such sensors may be connected in parallel with the chip detector monitoring circuit. The present invention is a test circuit which will, upon the turning on of the power to an aircraft electrical system, both provide an indication of monitoring circuit continuity and adequate oil level at the chip detector as determined by a chip detector oil level sensor.
In prior art, test circuits for chip detector monitoring circuits, the test circuit shorts or closes the circuit at a location adjacent to the chip detector for an arbitrary time period, as it does for all other circuits which are being tested at the same time. Although the time period is arbitrary in at least one prior art application it is fifty seconds which shall be used for purposes of describing the present invention. Thus, for a period of fifty seconds, beginning at power up, an array of warning lights will illuminate during the fifty-second time period. The aircraft crew scans the instrument panel looking for lights which fail to illuminate thus indicating a problem with the particular circuit associated with that light. There may be a separate system which tests the warning lights or other illuminating devices to ensure that they are operating properly. After the fifty-second time period the test is completed by removing the short resulting in lights to being extinguished.
After the test, the actuation of a warning light indicates that that particular monitoring circuit detected a fault, e.g., it would indicate that the chip detector monitoring circuit has detected a chip or an accumulation of chips of excessive size and that the aircraft crew should take appropriate action. The test circuit of the present invention will, during a test at start up, provide an indication of one or both of the following conditions by causing a single light to indicate if there is: (1) lack of electrical continuity of the chip detector monitoring circuit or (2) inadequate oil level at the chip detector.
If there is no continuity between the lamp and the chip detector and continuity testing circuit, the panel lamp will not illuminate upon aircraft power-up or after the 50 second test period. The lack of a lit lamp will alert the pilots to a problem. If there is continuity in the circuit, aircraft manufacturers have chosen two alternative methods to indicate to the pilots that there is a problem with chip detector oil level. In a first manner, the panel lamp will illuminate during the test period to indicate continuity, but will remain on after the test period to indicate a problem with the oil level. The illumination of the lamp during the test period and it not being illuminated after the end of the test period indicates that the circuit has continuity and that the oil level at the detector is adequate. In the second manner which may be chosen by some aircraft manufacturers, low oil level at the chip detector will prevent the panel lamp from illuminating at all even during the test period. This manner does not distinguish between a lack of continuity and a low oil level but does alert the pilots that there is a problem.
The present invention could be adapted so that a problem is indicated by having the light illuminated and that the lack of a problem is indicated by the light not being illuminated. Use of this mode would require that the continuity test be made after a test confirming the operability of the lights or lamps. Which of the two indicating modes is a matter of choice.
In a first embodiment of the invention, the first manner discussed above of indicating low oil level is implemented. In a second embodiment of the invention, the second manner discussed above of indicating low oil level is implemented.